1. Field
The present invention relates to an apparatus for injecting liquid crystal into a hollow fiber or a planar waveguide and a method thereof, and more particular, to an apparatus for injecting liquid crystal into a hollow optic fiber after making the inside of the long hollow fiber vacuous to overcome resisting force generated by a surface tension of the liquid crystal and an inside surface of the hollow fiber, and a method thereof.
2. Discussion of Related Technology
Since a liquid crystal is in a liquid state and includes large size molecules having electric aeolotropy, the liquid crystal has variable double refraction characteristics changed according to arrangement of the molecules. Therefore, the liquid crystal has been widely used not only to a display device such as a television or a computer monitor but also to various optical devices using polarized waves such as a polarizer and a quarter wave retarder.
An optical communication system and an optic fiber sensor system generally employ Bulk Optics as liquid crystal optic components. Basically, light is extracted from the optic fiber and the extracted light is collimated. The collimated light is passed through small size films or boxes, and then the passed light is re-injected into the optic fiber. Since the liquid crystal technology using the Bulk Optics extracts and reinserts the light, insertion loss of light is inevitable. Also, the liquid crystal technology using the Bulk Optics is badly influenced by temperature variation and external environment because it requires a mechanical device that arranges light beam in a spatial domain.
Recently, there are many researches in progress to develop a device using liquid crystal for compensating polarization mode dispersion (PMD) that is a major factor of limiting high speed optical transmission faster than 10 Gbps. For example, if a PMD compensating unit is embodied using the liquid crystal optic fiber, the insertion loss of light can be reduced drastically because the PMD compensating unit is basically a kind of the optic fiber. Furthermore, a polarizer installed between the liquid crystal optic fiber and an optical transmission line can be embodied with the same liquid crystal optic fiber. Accordingly, the shape of the PMD compensating unit can be simplified. Moreover, the reliability of the device is improved and the manufacturing cost is reduced since a mechanical device for light collimation is not required.
In case of the PMD compensating unit using a liquid crystal optic fiber, the length of the optic fiber using in the PMD compensating unit is decided according to a maximum value of PMD to compensate and a type of a liquid crystal. The length of the liquid crystal optic fiber may need to be several meters or several tens meters to compensate PMD of several tens ps.
In order to inject the liquid crystal into a hollow optic fiber, one end of the optic fiber soaks in a container having liquid crystal and other end of the optic fiber is straight up or slightly inclined. Then, the liquid crystal is naturally inserted into the hollow optic fiber by capillarity.
Although such a method of inserting using the capillarity is very simple, the length of the optic fiber is limited to several centimeters and it takes several days to insert the liquid crystal into the hollow optic fiber. Therefore, it is impossible to insert the liquid crystal into the hollow optic fiber of the several meters or the several tens meters. It is also impossible to manufacture a PMD compensating device requiring the hollow optic fiber of the several meters and the several tens meters.
As described above, insertion of liquid crystal into long hollow optic fiber is major factor to apply the liquid crystal optic fiber to the PMD compensating device.
One of difficulties for inserting the liquid crystal into the long hollow optic fiber is dynamic variation. The dynamic variation arises when the liquid crystal flows in a pipe having a diameter of several micrometers. That is, dynamics of the liquid crystal flowing in the pipe of several micrometers is completely different from that of the liquid crystal flowing in a pipe having a diameter of several centimeters or server meters. Such a dynamic variation is called as a micro fluid dynamics. The dynamic variation arises by interaction between the liquid crystal molecule, which is electric dipole, and the surface of the pipe. The dynamic variation becomes un-ignobrale if the diameter of the pipe is several times larger that the liquid crystal molecule. That is, the dynamics of the liquid crystal molecule will be badly influenced by the surface of the pipe. When the liquid crystal flows through the pipe having the diameter of several micrometers, the pulling power of the surface of the pipe becomes greater than gravity. Since the surface of the pipe strongly pulls the liquid crystal, it is very difficult to flow the liquid crystal through the pipe. Therefore, there is a great demand of developing an apparatus and a method of injecting the liquid crystal into the hollow optic fiber to overcome the interaction between the liquid crystal and the inside surface of the optic fiber in order to inject the liquid crystal into the long hollow optic fiber having a diameter of several micrometers.
The discussion in this section is to provide general background information, and does not constitute an admission of prior art.